Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Qual é o D 50 quando o D 43 é r 43?
 ###Tabelas: CREATE TABLE analytical_table (analytical_table_id AUTO_INCREMENT PRIMARY KEY, State VARCHAR, Votes INT, Votes since 1856 INT, Democratic votes INT, D votes since 1856 INT, % of D votes VARCHAR, D % since 1856 VARCHAR, Republican votes INT, % of R votes VARCHAR, R % since 1856 VARCHAR, Other votes INT, O votes since 1856 INT, % of O votes VARCHAR, O % since 1856 VARCHAR) CREATE TABLE senate_composition_before_the_elections (senate_composition_before_the_elections_id AUTO_INCREMENT PRIMARY KEY, D 50 VARCHAR, D 49 VARCHAR, D 48 VARCHAR, D 47 VARCHAR, D 46 VARCHAR, D 45 VARCHAR, D 44 VARCHAR, D 43 VARCHAR, D 42 VARCHAR, D 41 VARCHAR) CREATE TABLE episodes (episodes_id AUTO_INCREMENT PRIMARY KEY, # (season #) VARCHAR, No. (episode #) VARCHAR, Title VARCHAR, Directed by VARCHAR, Written by VARCHAR, Original air date VARCHAR, Prod. code VARCHAR) CREATE TABLE total (total_id AUTO_INCREMENT PRIMARY KEY, Rank VARCHAR, Nation VARCHAR, Gold INT, Silver INT, Bronze INT, Total INT) CREATE TABLE historical_population (historical_population_id AUTO_INCREMENT PRIMARY KEY, Rank VARCHAR, County VARCHAR, % (1960) INT, % (2000) INT, % (2040) INT)  
SELECT D 50 FROM senate_composition_before_the_elections WHERE D 43 = r 43